BG63215B1 - Desulphurization mixture based on calcium carbide - Google Patents

Abstract

The desulphurizatuion mixture for cast-iron purification consists of at least 50 wt. % powder calcium carbide of granulometric grain size <0.2 mm, from 1 to 20 wt. % powder magnesium or granules of grain size <0.8 mm and from 5 to 15 wt. % powder aluminium or granules with grain sizes <0.8 mm, optionally other powder additives such as calcium oxide, calcium carbonate, carbon-containing products and/or means for coating the grains. The total quantity of the additives is up to 30 wt. %. The iron losses in the process of desulphurization of the cast iron are reduced when applying the mixture. 2 claims

Description

Technical field

The invention relates to a desulphurising mixture of calcium carbide based for injection by means of a jet in cast iron obtained in a blast furnace before passing it into the converter.

BACKGROUND OF THE INVENTION

Although the cast iron and slag flow separately from the blast furnace, there is still a significant amount of slag left in the buckets, in the order of 5 kg / t. On the other hand, a desulphurisation product is obtained from the sulfur-rich slag, which must be separated from the metal before it goes to the converter. At this stage, the removal of the slag is done mechanically, which causes loss of metal due to entrainment.

It is known that the preparation of a liquid desulphurization product can significantly reduce the metal losses when clearing the slag in the buckets. To do this, sodium carbonate is added to the metal bucket before cleaning, which decomposes to sodium oxide with a melting point of 1132 ° C. The resulting slag contains sodium, which is harmful to the environment, so other solutions are sought to reduce metal wastage.

The addition of desulphurizing agents of reducing metals such as aluminum or magnesium is also known to accelerate desulphurization by eliminating oxygen dissolved in cast iron (FR 1168646). FR 2317361 describes a desulfurizing agent based on a powder of calcium carbide, calcium cyanamide or calcium oxide, to which 0.5 to 3.5% aluminum or magnesium powder of the same granulometry is added.

It is also known from EP 0398674 the addition of low melting point calcium aluminate to calcium carbide to obtain more complete desulfurization of the mixture by continuously injecting a certain amount of the desulfurizing mixture.

SUMMARY OF THE INVENTION

The desulphurisation mixture according to the invention is based on micronized calcium carbide powder, also containing magnesium and aluminum powders, the proportions of the components being so determined that it allows a significant reduction of the iron losses during desulfurization. The mixture contains at least 50% by weight. calcium carbide powder with a particle size <0.2 mm, from 1 - 20% magnesium powder with a particle size <0.8 mm and from 5 - 15% aluminum powder with a particle size <0.8 mm, where appropriate contains other powder additives such as calcium oxide, calcium carbonate, carbon containing products and / or coating agents in a total amount of up to 30%.

The mixture according to the invention is based on technical calcium carbide, which generally contains about 80% by weight. calcium carbide, the remainder being calcium oxide, with at least 25% of the particles having a particle size of 0.1 to 0.2 mm. To this carbide may be added calcium oxide, calcium carbonate, carbon-containing products such as carbon black, graphite or anthracite, or other products intended to improve the flowability of the mixture or to release gas, which allows a good distribution of the desulfurizing agent in the liquid cast iron. Up to 2% kernel cover, for example hydrogenated castor oil, as described in EP 0511121 to the applicant may also be added. Magnesium is added to the mixture in the form of powders or granules of pure metal, or a magnesium-based alloy with a particle size <0.8 mm. Also, the grains may be coated as well as those of calcium carbide with an organic product, for example based on saturated aliphatic acids, or their esters, as described in EP 0485309 to the applicant.

Finally, 5 to 15% of aluminum or aluminum alloy powders or granules are added to the mixture, which can also be coated with a product such as that used for magnesium. The mixture of powders or granules is prepared in a mixer operating in an inert atmosphere such as nitrogen.

The mixtures according to the invention have efficacy as desulfurizing agents at least equal to mixtures in which aluminum is replaced by an equal amount of magnesium and therefore does not lead to excess consumption of the product, which is unexpected, since aluminum is not magnesium back in itself. its a desulfurizing agent. On the other hand, more fluid slag is formed, easier to clean and slag cleaning is associated with too low iron losses. In addition, the slag does not contain any product that pollutes the environment, such as sodium oxide.

Examples of carrying out the invention

Example 1 (comparative).

The efficiency of desulphurisation and the loss of iron of two desulphurisation mixtures of the known level based on technical calcium carbide were compared, the first containing 20% by weight. magnesium granules, the second 20% by weight. calcium oxide aluminate powder with a third mixture according to the invention containing 10% magnesium granules and 10% aluminum granules.

The test is carried out in buckets containing 300 t of cast iron. The initial sulfur content is about 250 ppm, while its final sulfur content is 55 ppm. The efficiency of a desulfurizing agent is determined by the ratio of moles of iron as a loss of cast iron to moles of injected desulfurizing agent, i.e., in this case moles of calcium carbite and magnesium, since aluminum is not in itself a desulfurizing product. The loss of iron is determined by the ratio of the mass of cast iron contained in the slag to the mass of cast iron contained in the desulphurization bucket.

For the three mixtures, the following results are obtained, which are averaged from 20 experiments performed under the closest possible conditions.

Table

The mixture Performance% Loss of iron,% 1 22 1.1 2 18 0.9 3 23 0.3

Comparing the results for mixtures with 3, it is found that their effectiveness with respect to desulfurization is comparable, but with respect to the losses of iron, the use of mixture 3 results in a reduction of 15 of these losses 3.7 times.

Comparing mixtures 2 and 3, it is unexpectedly found that aluminum leads to desulfurization significantly more efficiently, and is increased 3-fold over mixture 3, when 20 could be expected to have similar results, since the aluminate inserts alumina into the slag and aluminum is oxidized in cast iron to form alumina which is dissolved in the slag.

Claims (1)

CLAIMS 1. A desulphurisation mixture for injection in calcium carbide-based cast iron, characterized in that it contains at least 30% by weight. calcium carbide powder with a particle size <0.2 mm, 1 - 20% magnesium powder or granules with a particle size <0.8 mm and from 5 - 15% aluminum powder or granules with a particle size <0.8 mm, optionally with other powdered additives such as calcium oxide, calcium carbonate, carbon-containing products and / or grains, with a total amount of additives of up to 30%. A mixture according to claim 1, characterized in that <25% of the calcium carbide grains have a particle size of 0.1 - 0.2 mm.